This invention relates to holographic display elements used for authentication and to the use of bar codes for identification and authentication.
In order to discourage the fraudulent manufacture of information cards, such as credit cards, card manufacturers produce a card that includes a holographic display. A hologram is a recording of an interference pattern between two beams of light, usually referred to as the signal beam and the reference beam. The signal beam usually includes the image to be recorded, and the reference beam is a beam of light, usually of constant distribution, i.e., plane of spherical wavefront. Typically, another reference beam, similar to the one used to record the hologram, is used to reconstruct the signal beam, which then produces an identifiable image. For many holograms, one cannot identify an image without reconstruction.
The holograms typically used on credit cards are what are known as rainbow holograms. They are produced by placing the image to be recorded near the surface of the holographic substrate during recording. These holograms are visible in ordinary, white light and should be familiar to most holders of credit cards. The rainbow hologram can be mass produced on sheets of metalized embossing substrate, and stamped onto credit cards. Such holograms are a deterrent to counterfeiting because the production requires an expensive manufacturing investment.
Some identification cards, e.g. some library cards, provide individual information about a cardholder with a code such as a bar code symbol. Bar code symbols are formed from bars or elements that are typically rectangular in shape with a variety of possible widths. The specific arrangement of elements defines the character represented according to a set of rules and definitions specified by the code or "symbology" used. The relative size of the bars and spaces is determined by the type of coding used, as is the actual size of the bars and spaces. The number of characters per inch represented by the bar code symbol is referred to as the density of the symbol. To encode a desired sequence of characters, groups of elements are concatenated together to form the complete bar code symbol, with each character of the message being represented by its own corresponding group of elements. In some symbologies a unique "start" and "stop" character is used to indicate where the bar code begins and ends. A number of different bar code symbologies exist. These symbologies include, e.g., UPC/EAN, Code 39, Code 49, Code 128, Codabar, Interleaved 2 of 5, etc.
In order to increase the amount of data that can be represented or stored on a given amount of surface area, several new bar code symbologies have recently been developed. One of these new code standards, PDF417, introduces a "two-dimensional" concept by stacking rows of characters vertically instead of extending the bars horizontally. That is, there are several rows of bar and space patterns, instead of only one row. Thus, bar codes include not only the traditional rectangularly-shaped bars and spaces, but any form of symbol in which different portions of the symbol have different light reflecting characteristics.
Bar codes are scanned to transform the graphic symbol elements into electrical signals, which are then decoded into characters. A scanning system uses a light source, typically a gas or semiconductor laser, which is directed to the symbol or bar code by a lens or other optical components. The scanner functions by repetitively scanning the light beam in a path or series of paths across the symbol. Scanning systems also include a sensor or photodetector which detects light reflected from the symbol. A portion of the reflected light is detected and converted into an electrical signal, and electronic circuitry or software decodes the electrical signal into a digital representation. The symbol is decoded according to the coding technique used, e.g., the Uniform Product Code (UPC) on many supermarket items.